On 06/21/2016 08:16 AM, Kevin Wolf wrote: > Am 14.06.2016 um 23:30 hat Eric Blake geschrieben: >> It makes more sense to have ALL block size limit constraints >> in the same struct. Improve the documentation while at it. >> >> Signed-off-by: Eric Blake <ebl...@redhat.com> >> >> ---
>> struct BlockLimits {
>> + /* Alignment requirement, in bytes, for offset/length of I/O
>> + * requests. Must be a power of 2 less than INT_MAX. A value of 0
>> + * defaults to 1 for drivers with modern byte interfaces, and to
>> + * 512 otherwise. */
>
> No, a value of zero probably crashes qemu. The defaults apply when they
> aren't overridden by the driver, but this field is always non-zero.
>
Then why does block.c have:
--- a/block.c
+++ b/block.c
@@ -1016,7 +1016,7 @@ static int bdrv_open_common(BlockDriverState *bs,
BdrvChild *file,
assert(bdrv_opt_mem_align(bs) != 0);
assert(bdrv_min_mem_align(bs) != 0);
- assert(is_power_of_2(bs->request_alignment) || bdrv_is_sg(bs));
+ assert(is_power_of_2(bs->bl.request_alignment) || bdrv_is_sg(bs));
That says that if bdrv_is_sg(bs), we can indeed have request_alignment
be 0. Should I track that down and fix it first, so that
request_alignment is always nonzero? If so, is using '1' for
bdrv_is_sg(bs) the ideal solution?
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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